The present invention relates to bi-directional amplifiers, and more particularly to bi-directional amplifiers using junction field effect transistors (JFET).
Amplifiers are commonly found in numerous types of electronic equipment. They are, for example, basic building blocks in receiver and transmitter design. In certain applications, it has been found desirable to reduce the number of electronic components by providing amplifier systems which are bi-directional, that is, they amplify a signal flowing in either direction through the amplifier system. Bi-directional amplifier systems are known, for example, in voice frequency amplification, closed circuit television video and control signal amplifiers and in digital data amplifiers. Such devices typically have separate amplification means for each direction of signal travel and share some of the non-amplifier reversible components, such as filters and mixers. Accordingly, such devices do not reduce the number of amplifiers but do provide more convenient packaging. (See, U.S. Pat. No. 3,889,072 to Stewart, U.S. Pat. No. 4,714,959 to Pshtissky and U.S. Pat. No. 3,882,274 to Vice, et al.)
A JFET is essentially a voltage amplifier consisting of a conducting channel between two nearly identical junctions, typically labelled drain and source. The direction of current flow through the channel depends on the DC potential between the drain and the source, provided the gate (controlling the channel) is properly biased. When used in a common gate configuration, the output current and input current of the JFET are the same. Voltage gain is achieved by providing a higher impedance at the drain than at the source. Typically, an impedance matching circuit is provided to match the high impedance at the drain to the load. The low impedance at the source of the JFET can either be connected directly to the input if the impedance match is satisfactory, or through a matching circuit, if required. Thus, the JFET must be provided with appropriate impedance matching circuitry to operate. Such circuitry operates to provide a specific impedance match and thus operates in only one direction.
One direction amplifiers using JFETs with appropriate impedance matching circuits are known in the art. (See, U.S. Pat. No., 4,163,198 to Berning, U.S. Pat. No. 4,214,215 to Mellen, et al., U.S. Pat. No. 4,591,803 to Saleh, U.S. Pat. No. 4,598,253 to Reindel, et al., U.S. Pat. No. 4,639,683 to Counts, et al. and U.S. Pat. No. 4,713,626 to Susak, et al.) It is not known, however, to provide versatile impedance matching circuits to be able to use a JFET in a bi-directional amplifier.
It is accordingly an object of the present invention to provide a novel bi-directional amplifier that obviates the problems of the prior art and uses a JFET to reduce the number of amplifiers required.
It is another object of the present invention to provide a novel bi-directional amplifier that uses the symmetrical properties of the JFET to make the designation of drain and source in the JFET dependent on the direction of signal flow through the amplifier.
It is yet another object of the present invention to provide a novel bi-directional amplifier with versatile impedance matching circuits at the two ]unctions of a JFET to make the JFET operable as an amplifier in both directions.
It is a further object of the present invention to provide a novel method for amplifying a signal in which a single JFET amplifies the signal as it flows in either direction through the JFET.
These and many other objects and advantages will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.